In the vehicle body lower portion structure disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2005-212503 (Patent Document 1), floor cross members and extended portions of front side members intersect as seen in plan view, and the both nip a floor panel therebetween and are fastened by bolts and nuts. Due thereto, the separation strength at the joined portions of the front side members and the floor cross members can be improved.
Note that, generally, the front end portion of a floor member, that extends in the vehicle longitudinal direction, is joined to the rear end portion of the extended portion of the front side member. Further, plural floor cross members are provided in the vehicle longitudinal direction. The floor cross member, that structures the vehicle rear side mounting portion of a vehicle seat, intersects the floor member as seen in plan view.